Foaming presents a serious problem in many industrial lubrication applications especially in various types of engines operated at high speed and which are lubricated with mineral oil. For example, foaming is particularly a problem in conventional internal combustion engines, turbines, gear sets and for various aircraft engines operated at high speed. Without foam inhibitors severe churning and mixing of the oil with air allows foam to form and under continuous use the foam, a mixture of air and oil may overflow from the lubrication system leading to eventual failure of the machine or parts causing expensive breakdowns or costly maintenance problems.
Among the foam inhibitors known to be effective in mineral oils are organo-silicone, polymeric compositions referred to as silicone-polyglycol copolymers, silicone polyethers or silicone polyether polymers, among other names. A group of these compositions are disclosed in U.S. Pat. No. 2,834,748 and are designated as siloxane-oxyalkylene block copolymers. Unfortunately, these copolymers, while effective in actual operation, have certain deficiencies which complicate their formulation and storage.
For instance, since these polymers are not soluble in mineral oils to any appreciable extent, they must be added to oil in the form of solutions in low-boiling solvents, such as benzene or its homologues. Further, because of their insolubility in oil, they form dispersions which tend to stratify in storage over considerable periods of time, thereby degrading the anti-foam effect. In addition, some of the desired polymers are sensitive to moisture and become non-homogeneous in contact with air over relatively long periods of storage.
Thus, the objects of this invention are to convert siloxane-oxyalkylene block copolymers to an oil-soluble form in order to improve their utility as foam inhibitors, and at the same time to improve their resistance to degradation by moisture.
Recently it has been found that the settling out or stratification problems can be overcome by forming a complex (or stable admixture) of the above copolymers or similar types of siloxane-type copolymers with certain alkylated phenols. Not only do the complexes formed stabilize the copolymers but even more surprising the alkyl-phenol-complexed copolymers usually show substantially enhanced defoaming properties in mineral oil-based lubricants compared to the untreated (non-complexed) copolymers. The enhancement of anti-foaming in mineral oil systems by forming the alkyl phenol complex is quite unexpected in that:
1. The alkylated phenols used to complex the copolymers used along are not anti-foamants in mineral oil.
2. The untreated "siloxane" copolymers, as described in U.S. Pat. No. 2,834,748, include at least one polyoxyalkylene chain preferably three polyoxyalkylene chains in the molecule. Yet polyglycols alone or polyglycols admixed with alkylphenols to form complexes are not anti-foamants in a mineral oil system, within the concentration range in which the solubilized copolymers are effective.
3. The admixing of said copolymer with alkylated phenol, presumably to form a stabilizing complex (or stable admixture) takes place at room temperatures and atmospheric pressures using standard equipment and routine laboratory techniques. In fact, no special order of addition of the alkylated phenol to substrate is required.
A convenient method for determining the ratio of alkylphenol to silicone substrate required to achieve solubility in a given mineral oil is to add the alkylphenol slowly with vigorous agitation to a mixture of about two parts mineral oil to one part silicone substrate. When a clear, bright solution is observed, the minimum ratio of silicone to alkylphenol is now known. This concentrate can be added to the same or different mineral oils to achieve whatever concentration of polymer is desired. Alternatively once the ratio of alkylphenol to silicone necessary to achieve oil solubility has been determined, a complex containing only silicone and alkylphenol can be prepared for subsequent use as an anti-foamant or for other uses, as desired.
In the usual practice, each part by weight of polymeric silicone substrate to be stabilized having the following characteristics:
Average molecular weight - 1000 to 5000 PA1 Silicon (% by weight) - 4 to 30 PA1 Dimethyl siloxane (% by weight) - 10 to 95 PA1 Identity of Polyglycol - Ethylene glycol, or ethylene-glycol-propylene glycol copolymers PA1 Polyglycol (% by weight) - 90 to 5 PA1 Average molecular weight - 1500 to 3000 PA1 Silicon (% by weight) - 10 to 30 PA1 Dimethyl siloxane (% by weight) - 20 to 50 PA1 Identity of Polyglycol - 50% polyethylene 50% polypropylene PA1 Polyglycol (% by weight) - 50 to 80
is admixed with from 1-20 parts of petroleum (mineral) oil having a viscosity at 100.degree.F of about 50 centistokes and at least one part by weight of alkylated phenol is added with stirring, wherein said alkylating group or groups containing a total of from 4 to 30 carbon atoms, until a visually clear, homogeneous and stabilized complex of polymeric substrate and alkylated phenol in mineral oil is produced.
In the favored practice each part by weight of a polymeric silicone-polyglycol substrate to be stabilized for storage and having the following characteristics:
is admixed with from 2-10 parts petroleum (mineral) oil and at least 2 to 8 parts by weight of alkylated phenol, wherein said alkylating group or groups contain a total of from 4 to 30 carbon atoms until a visually clear, homogeneous and stabilized complex of polymeric substrate and alkylated phenol in mineral oil is produced.
In order to provide the scope of the inventive concept the following additional disclosure is submitted.
A. Alkylated phenol-type compound
This is the generic term used to designate the class of complexing agents employed to improve the storage stability of the mineral oil-silicone/polyglycol copolymer compositions and, in most instances, the foam-inhibiting properties of the copolymers when dispersed in mineral oil. While no specific mechanism is relied on for patentability, nor postulated to explain how or why the copolymers and alkylated phenols function better together than when employed singly, it is believed that a complex is formed between the phenolic hydrogen and the polyglycol oxygen which potentiates the foam inhibition of the copolymers by enabling them to be more uniformly dispersed throughout the oil. The same mechanism is thought to be responsible for their oil solubility and improved storage stability.
Illustrative alkylated phenols are chosen from either or both mono- and dinuclear aromatics that contain one hydroxyl group and an alkylating group or groups containing a total of between 4 and 30 carbon atoms, arranged in either branched chains or straight chains. The alkylated phenol-type compound can be in the form of a relatively pure discrete single compound or in the form of blends or mixtures of one or more alkylated phenols.
Illustrative preferred complexing agents are the butyl phenols, the pentyl phenols, the hexyl phenols, the heptyl phenols, the octyl phenols, the nonyl phenols, the decyl phenols, the undecyl phenols and the dodecyl and tridecyl phenols. Especially preferred are the alkylated phenols in which the alkyl groups contain from 9 to 16 carbon atoms and are branched rather than straight chain.
B. Polysiloxane-Polyglycol Polymers
This is the generic nomenclature used throughout this application for the substrate whose stability is to be improved. These copolymeric substrates which lend themselves to treatment for improved stability have been empirically derived polymers selected from the group consisting of Siloxane-Oxyalkylene Block copolymers of the general formula disclosed in U.S. Pat. No. 2,834,748, Col. 2 as: EQU (R)'(SiO.sub.3).sub.x (R.sub.2 SiO).sub.y [CnH.sub.2n O).sub.z R"].sub.a [R"'].sub.3x-a
where x is an integer and represents the number of trifunctional silicon atoms bonded to a single monovalent or multivalent hydrocarbon radical R', a is an integer and represents the number of polyoxyalkylene chains in the block copolymer; y is an integer having a value of at least 3 and denotes the number of difunctional siloxane units, n is an integer from 2 to 4 denoting the number of carbon atoms in the oxyalkylene group and z is an integer having a value of at least 5 and denotes the number and length of the oxyalkylene chain.
The above polymers can be formed by reacting a polyalkoxy-polysiloxane having at least three (3) alkoxy groups attached to a polysiloxane chain with a monohydroxyl polyoxyalkylene mono-ether by an exchange reaction wherein at least part of the alkoxy groups attached to the polysiloxane are replaced by polyoxyalkylene mono-ether radicals and the alkoxy groups removed as the corresponding alkanols.
While the block copolymers of this invention usually conform to the preceding chemical composition and method of manufacture, no need is seen to be limited thereto since any copolymer consisting of a silicone moiety and a polyalkylene glycol moiety can be stabilized by the disclosed process.
C. Condition required for the Treatment of the Siloxane-Polyalkylene Glycol Copolymers with Alkylated Phenols to improve their Stability
Of the conditions required for the stabilizing of the polydimethylsiloxane-polyalkylene glycol copolymers, (temperature, time of mixing, order of addition, ratio of components), none is critical to success except the latter. As previously indicated, the alkylated phenol should be employed in weight excess, preferably from 1 to 20 parts by weight of said phenol to each part by weight of copolymer. The ratio will vary depending on the particular polymer and alkylated phenol (alkyl phenol) involved.
The usual procedure where it is desired to make an oil concentrate, is to add the copolymer to the mineral oil with continuous stirring and then to add the alkylated phenol slowly, usually between 20.degree.C and 50.degree.C, until a homogeneous complex that is clear to the eye is attained. The term complex as used throughout this disclosure refers to that of a group of obviously related units of which the degree and nature of the relationship is imperfectly known. Additional alkylphenol beyond that necessary to achieve clarity is not harmful but is usually unnecessary and therefore to be avoided.
If it is desired to eliminate the mineral oil from the complex, and provided the proper ratio of polymer to alkylphenol is already known, the two components can be simply mixed by conventional stirring at 30-50.degree.C.
The time required for preparation of the complex cannot be set forth precisely, since the copolymer and alkylated phenol employed, the type of agitation used and temperature at which complex formation is undertaken all vary from instance to instance. However, in most instances the time required will be between a few minutes up to less than one half hour.
D. Hydrocarbon Oils
As used throughout this application the terms "mineral oil", "hydrocarbon oils" are synonymous with "petroleum oils". Mineral oils which are subject to foam inhibition when mixed with the inventive complexes are paraffinic oils, naphthenic and asphaltic oils having kinematic viscosities at 100.degree.F from about 10 centistokes to about 5000 centistokes.
E. Characteristics of the Copolymer Substrates to be Complexed.
______________________________________ Operable Preferred Range Range Molecular Weight 1000 - 5000 1500 - 3000 % By Weight of Silicon 4 - 30 10 - 25 % By Weight Dimethylsiloxane 10 - 95 20 - 50 % By Weight of Polyglycol 90 - 5 50 - 80 Type of Polyglycols -- polyethylene glycol and ethylene- glycol-propylene glycol copolymers. ______________________________________
Table I shows characterizing tests on the polymers employed in the subsequent examples. It will be noted that all are insoluble in mineral oil, as evidenced by the fact that a 0.1% by weight blend of polymer in a paraffinic oil is cloudy at 25.degree.C.
TABLE I __________________________________________________________________________ CHARACTERIZATION OF COPOLYMERS COPOLYMER IDENT. A B C D E F G H __________________________________________________________________________ OIL SOLUBILITY.sup.(6) Insol. Insol. Insol. Insol. Insol. Insol. Insol. Insol. MOLECULAR WEIGHT 2360 3050 2730 2380 1440 1860 1340 1850 ANALYSIS (WT.) SILICON, % 6.8 7.4 4.7 13.4 9.5 9.3 22.5 26.6 CARBON, % 53.0 53.4 54.9 49.8 46.5 30.6 43.4 36.9 HYDROGEN, % 9.5 9.7 9.2 9.3 9.1 8.6 8.9 6.2 OXYGEN (BY DIFFERENCE) 30.7 29.5 31.2 27.5 34.9 51.5 25.2 30.3 APPROXIMATE COMPOSITION.sup.(1) DIMETHYL SILOXANE POLYMERS 20 20 12 35 30.sup.(2) 30.sup.(3) 70 90 POLYGLYCOL POLYMERS.sup.(5) 80 80 88 65 70 70 30.sup.(4) 10 __________________________________________________________________________ .sup.(1) BASIS ELEMENTAL ANALYSIS .sup.(2) LOWER M.W. SILICONE MOIETY .sup.(3) HIGHER M.W. SILICONE MOIETY .sup.(4) POLYPROPYLENE GLYCOL .sup.(5) ALL POLYETHYLENE OR POLYETHYLENE/POLYPROPYLENE EXCEPT COPOLYMER G. .sup.(6) AT 0.1% BY WT., WILL NOT GIVE A CLEAR BLEND IN PARAFFINIC MINERA OIL AT 25.degree.C.
In order to disclose this invention in the greatest possible detail, the following illustrative examples are set forth. Unless specified otherwise, all percentages and parts are by weight rather than volume, and all temperatures are in degrees centigrade.
The following is a more detailed characterization of the base oils referred to in the subsequent examples:
DESIGNATION BASE OIL A BASE OIL B BASE OIL C BASE OIL TYPE Highly Solvent Solvent Refined Moderately Refined Paraffin Paraffin Base Solvent re- Base Neutral oil Residual Oil fined Neut- ral Oil __________________________________________________________________________ Viscosity, 69.6 717.1 20.8 Kinematic at 100.degree.F., cs. Viscosity Index 103 82 63 Pour Point, .degree.F. +5 0 +15 Gravity, API 29.2 24.2 28.5 __________________________________________________________________________